To help countries such as the US to get to Europe and the Pacific, and conversely those nations to other ocean barrier continents how about SHIPPING LANES?
A shipping lane is just like a road but crosses the ocean and the intent is would help path AI for merchant marine for invasions and travel.
RUGES mod for SR2020 uses "ferries" which are an invisible bridge to cross rivers. If such were consecutively strung together and called "shipping lane," and were restricted to the Merchant Marine, the thought is it might help path traffic across the oceans better.

We shoul'd be able to raid shipping of all major regions, not just the UK. Now we can not raid japanese (but why we woul'd do that at all?) or US or Chinese merchants and that just don't feels right!

You can still raid, "shipping lane" would be just sort of an invisible road in the ocean to help path the AI across long distances, that is if the AI uses a road to path along across continents on land. I was trying to do it myself adding RUGEs ferry / tunnel consecutively on the 1936 map but cannot get it to show ingame.